A LEADING American divorce mediator will visit Washington this week to offer members of Congress advice on ending the "tiresome bickering" between Republicans and Democrats.

If US tabloids are to be believed, she may need to visit the White House first.

Michelle Obama's extended absence from Washington and a flurry of renewed speculation about the state of the first couple's marriage are threatening to overshadow her 50th birthday party at the White House on Saturday.

Not for the first time in their 22-year marriage the Obamas are approaching what should be a happy family milestone under a cloud of rampant tabloid innuendo, summed up by a National Enquirer headline: "World exclusive: Obama marriage explodes!".

The Enquirer has earned a measure of respectability in Washington with its reporting of political scandals - most notably its exposure of the double life of John Edwards, a former senator and once a Democratic presidential contender.

Yet its so-called bombshell Obama report was based on nothing more substantial than the vague allegations of an unnamed "Oval Office insider" who claimed the first couple "are now sleeping in separate White House bedrooms" - tame stuff compared with the adventures of the president's French counterpart Francois Hollande.

In one sense the report was partly right: Barack Obama returned to Washington from his Christmas break in Hawaii last week while his wife remained in Maui to spend more time with friends, reportedly at a holiday home owned by the media mogul Oprah Winfrey.

Before the Enquirer could detonate another bombshell, a White House spokesman offered a different explanation for Michelle's solo break: it was a birthday present from her husband.

"If you have kids, you know that telling your spouse that they can go spend a week away from home is actually a big present," said Jay Carney, the White House press secretary.

Mr Obama acknowledged long ago that his marriage to Michelle had had ups and downs as they coped with the pressures of dual careers - she was formerly a lawyer and a hospital administrator - and the arrival of their two daughters, Sasha and Malia.

The latest tabloid report appears to have been provoked by the notorious incident at Nelson Mandela's memorial service when Mr Obama and David Cameron posed for a selfie with Helle Thorning-Schmidt, the prime minister of Denmark - or as the National Enquirer described her, "a leggy blonde foreign leader".

Despite the speculation, the Obamas have succeeded in presenting a united front and, as their daughters have grown, many of their admirers have come to regard them as an inspirational family.

The White House rarely comments on the first couple's private life, and there was no official confirmation last week of where Michelle was staying in Hawaii, or when she intended to return.

Yet the security umbrella that surrounds the couple descended on the Winfrey estate where The Daily Caller, a Washington news website, claimed Michelle was staying with a small group of female friends including Valerie Jarrett, a senior White House adviser, and Gayle King, a television presenter and close friend of Winfrey.

Oprah once said of her Hawaii home that she had "never encountered anyone who doesn't love it ... we sip drinks inspired by whatever is fresh and delicious - mango, guava, pineapple, cucumber, basil. We sometimes ride horses to the top (of the mountain) to watch the moon rise over the ridge".

It sounded like a blissful escape for a hardworking first lady who has made no secret of her distaste for life under the microscope.

She may have a rough return to the political world this week, with her husband's enemies sure to seize on any hint of excessive birthday party consumption as evidence of presidential extravagance.

The need to demonstrate frugality may have been the reason for the letters "EBYC" at the end of the invitation: guests have been advised to "eat before you come" to the party, which merely promises "snacks & sips & dancing & dessert".

The lack of dinner has divided social commentators. "I don't think it's rude, but I do think it's a little ... different than what people are used to," said Lizzie Post, a writer on etiquette.

Andre Wells, a party planner, disagreed. "It seems like a very casual party, and she's turning 50," he said. "The older you get, I feel like you can say what you want."

Either way, the first lady will be aware her every public move will be watched for signs of marital discord.

The betting in Washington is that the Obamas will display nothing of the sort, and that Michelle's 50th birthday will be marked with plenty of love and laughter.